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The mysterious dark Least Bittern

Note: I have never personally seen a living Cory’s Least Bittern. In fact, only six or so have been seen during my lifetime. Most of what follows is based on a very thorough 1996 research paper by Ron Pittaway and Peter Burke (see References below). The illustration shown below is correct, based on specimens and video. The painting included in the Sibley Guide to Birds on page 58 is incorrect; it should be darker and more uniform, without white on the back, and with blackish bill. In addition, the text below the image in early printings of the guide is also incorrect, and should read: Extremely rare, reported only a few times since the 1950s.

The rare and enigmatic Cory’s Least Bittern was first collected in 1885 in Florida and described as a new species. Questions about its status as a species arose soon after, but in the 1890s it attained quite celebrated status as a very rare bird and was eagerly sought by collectors. In 1923 the AOU Checklist dropped it from the list of accepted species, and the combination of being demoted to color morph, and going from rare to essentially nonexistent over the next few decades, meant that by the 1970s few birders were even aware of its existence.

It is strikingly different from typical Least Bittern. The plumage is entirely dark, with most of the areas that are normally pale yellowish-buff being dark reddish-brown, and parts that are normally darker brown being black. Some parts that are normally pale buff (e.g. the undertail coverts) also usually become black on Cory’s. White marks at the shoulders and white lines on the back shown by typical males are absent on Cory’s.

Many Cory’s show patches of unpigmented white feathers, most often on the belly and legs, and may also show melanistic patches of black feathers elsewhere.

The bill of Cory’s is blackish, unlike the pale yellow-green of typical birds. The legs also appear darker olive-green based on the only available video (link below).

Adult males, adult females, and juveniles all show similarly dark plumage. Note that juvenile typical Least Bitterns are somewhat darker overall than adults, and can be confused with Cory’s by the over-eager, but a true Cory’s is much darker still. Downy young are also much darker in Cory’s, and even the eggs of Cory’s are reportedly darker.

No intermediate specimens are known, and O. E. Baynard (in Bent 1926) reported that dark birds mated with each other and not in mixed pairs, although the form has always been so rare the sample size for this claim must have been very small. No differences in structure or behavior have ever been reported.

A total of 38 specimens are known, with 22 of those from Ontario, mostly near Toronto, and mostly before 1900. Those marshes have since been destroyed, but apparently the demand for specimens of this rare bird was so high in the late 1800s that the population was essentially wiped out even before the marshes were destroyed.

Apr 2010, Pantanal, Brazil, video; the only known images of a living Cory’s Least Bittern! http://www.youtube.com/user/baco1970#p/search/1/-DraxAu98Vw

14 May 2012, Red Slough, OK, male, sight record, D. Arbour, (listserv posting) [And in that discussion another observer recalled a sighting from Oklahoma City “maybe 30-40 years ago” by John Newell]

It is interesting that records are concentrated around the Great Lakes, where the species is now very rare, and Florida. The few recent records are more widely scattered, but clearly this very rare color morph is still out there and should be watched for.

Teixera, D. M. and H. M. F. Alvarenga. 1985. The First Recorded Cory’s Bittern (lxobrychus “neoxenus”) from South America. Auk 102: 413-414. pdf here: http://elibrary.unm.edu/sora/Auk/v102n02/p0413-p0413.pdf – details of the first South American record 13 May 1967 near Sao Paulo, Brazil.

Notes

Thanks to Ron Pittaway for all of his work on this bird, and Gerald Oreel for alerting me to references.

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Comments

Hi – Barkhamsted CT, We own 60 acres with a large pond ajacent to a marshy area. Tonight a large red tail swooped down and landed in a dead pine near the pond and over the swamp. A “coo – coo-coo’ came out as I was feeding the horse. A dark grey with maroon, rusty undercoating bird flew into the near by maple (50 yds). Funny flight pattern, odd color – we see a lot but I had never seen this one – run get the bird book! Says it is a bittern. there was no white on this bird either flying or roosting. Neck folded up once on the tree and it stayed for half hour. blended perfectly with grey bark of maple and new red leaves. 12 inches tall…I think it is a cory’s.

We will continue to look for it and hope to get a picture! Too dark to night. Warm regards, Heather and Will (9 years old) Robotham

in Goshen, CT –the first time I saw one, I was walking along the pond edge and it flew up from almost underneath me!! It landed on the small island in the pond and I just watched it all I could since I had never seen one before, Then it stayed while I went into the house and got field glasses and books and after it stayed, mostly hidden, visiting all week, the sound I could hear, (I googled extensively/checked books/saw images of dead ones) –really sure it is not green heron). Every year the bird would stop in for about a week and poke along the edge of our quiet pond–the second year, there were 2!! and then my friend said –there is a smaller one with them too!! yes, their baby!!! I saw the 3 of them. !!the last few years, just one came–today is May 22, 2018–and I think it/one is here right now–although it is raining out/hard to see–saw it jump up several times along pond edge and then fly to other edge of pond–sometimes it hangs around for a week–it usually comes a bit later in season than this

Regarding the Cory’s Least Bittern report from Toronto, Ontario, I wonder if the observer saw a Green Heron which also shows chestnut coloration. The “bright orange legs” are a good description of an adult male Green Heron in high breeding plumage. Was it seen in an open cattail marsh (bittern) or a swampy treed area (heron)? Cory’s Least Bittern is on the review list of recognizable forms for which the Ontario Bird Records Committee (OBRC) requires documentation.

Spotted one today 6.8.12 feeding in shallow, shady waters of the San Antonio river at Brackenridge Park. Got a good long look and his description fits info about Cory’s Least Bittern. (Sibleys and Nat Geo Field Guide) Dark beak (not in Sibley’s as noted above), dark gorgeous wine/brown neck into darker body. Yellow-green legs. Got photos to share, but not with me now. Have put word out to area bird experts and enthusiasts.

Hi Alicia, As Ron noted here recently, the possibility exists of confusion with Green Heron, and your description of the plumage colors and yellow-green legs fits well. Habitat and behavior is also a very strong clue. Least Bittern (light or dark morph) would only be expected in large expanses of cattails or other reedy marshy vegetation. These are generally sunny places, but the birds rarely come out into the open, and are usually seen just peeking out between stalks at the edge of a stand of reeds. The habitat you describe – “shallow shady waters” of a river sounds a lot better for Green Heron. I’d be happy to take a look at your photos to confirm the ID. Cheers, David

I have a couple of photos I took last week at the Buffalo National River in Arkansas of a bird that looks similar to the above descriptions and pictures on the videos posted above. They aren’t great quality, because I was some distance away and have a small digital camera. How could I send you the photos to look at?

I am editing the records from the collection of Elon Howard Eaton at Hobart and William Smith Colleges in Geneva, NY. I have a skin of a male Least Bittern collected by Eaton in Canandaigua, NY on 8 Sept 1898. The head has parted from the body at the neck. There is no white on the dark chestnut and charcoal back, the bill is amber, and the ventral side… throat-undertails is streaked rufous-buff with minimal white. In the spreadsheet (but not on the tag) is a note “possible Cory’s?” The collection was curated after Eaton’s death in the 30s by Theodore O’Dell so this note may have been his. A card catalog was kept but this may have been discarded after the spreadsheet was created several years before I arrived.

Thanks David. Even though it is darker overall than usual it looks like the Least skin in the link you sent. Just no visible white trim at the back. I don’t want to mess with it since we are about to donate the collection to the NY State Museum in Albany and these hundred+ year old skins are pretty fragile. I enjoy your work and this website.
Jim

saw a PAIR of Cory’s dark phase at my pond , they visited every day for a week or so, and on the last time we saw them, the fellow here says”quick, run, there is a smaller one” but immediately it went into the tall grass/vegetation along the edge and became invisible
the first one I saw-on the first day-flushed up from practically under me as I reached the pond edge-then it landed on the edge of the small island in pond center(it’s a small pond) then I studied it for a while, as I could tell it was a bittern, but had never seen a bird like it before, then I looked at Peterson’s and it was a dead ringer for Cory’s dark-definitely not green heron-it came for a week or so, brought its dark phase mate and a smaller one ,too-this is in Goshen/Cornwall,CT , about 1/2 mile from Mohawk Pond/Mohawk Mountain-so pretty undisturbed with wet areas here-we have frogs and crayfish and lots of vegetation up to pond’s edge

just looked at “specimen photos” in above reference-yep, exactly-unfortunately , I don’t own/use iPhone/camera-or I could have taken photo-sorry, I didn’t realize the rarity, I tried to contact Waterbury Republican “Talking Nature” Hanisek, didn’t even think to call Audubon Center-I am not a birder-just a nature observer on 4 1/2 acres, that are surrounded by Mohawk’s 1000 acres and a forested/riparian zone farm on 700 acres-nice location to enjoy nature-bitterns were seen here about 1 month ago-yesterday the large-maybe 45 pound snapper made his annual appearance at the pond-spent the day sunning his shell-and this morning I heard a bird, I have NEVER heard before-unable to see it, I’ll have to listen to my bird tapes till I match up the sound-very different sound-reminds me of an exotic jungle bird-kind of a resonating whoop-whoop-interesting

I just saw this strange bird last week and again this week in my pond and did not know what it was but it looks exactly like a Cory’s Least Bittern. I am located in North Royalton, Ohio, not sure if there have been an spottings in our state, but will try to get a photo of it the next time I see it to confirm that is what it is. Had the dark black and brown body with bright orange legs and long beak just like the picture.

I saw and managed to get some pretty good pictures of what to me looks an aweful lot like a Cory’s. I was in a Kayak in Parc National De Plaisance, Quebec, Canada. The bird I saw had a black cap, almost black back and wings, dark chestnut neck and chest, some white highlights lower on the belly, there were also some white tips in the wings. black bill, yellow eyes, yellow/orange feet and legs. I can email a pic for some clarification if I had an address to send to.

I am very excited to have observed what may be an extremely rare bird, a “Cory’s Least Bittern”. On July 6,2013 at almost 11:00 a.m., after several days of rain. I was looking out my window down at the pond on our small farm in rural Nicholas County, Kentucky, and noticed a very unusual bird. I could see this bird quite clearly, without disturbing him. I got out my Bushnell binoculars, so that I would be able to get a close up. This bird, at first appeared almost entirely black. Upon closer observation, I could see that the breast was a very dark chestnut color, no white or light feathers on this beautiful bird. The beak was as pictured above, although the legs were not the dark green pictured above, but had a dark yellow orange color. I can tell you that the bird that we saw was exactly the same bird that was on your link (above) on YouTube, titled “Cory’s Least Bittern at Pantanal” by Pantanal Bird Club. (It was the second video on the list)This bird was observed for about 1/2 hour, staying almost motionless in tall wet grasses, at the edge on the pond, in a clear area, not far from a forested area. This observation was so exciting. We are so privileged to have see such a rare sighting. Jim Gray

I am fairly certain that I spotted a Cory’s Least Bittern today, July 21, 2013, in Deltaville Va. at the Deltaville Mariner’s Museum around mid-day. At the time I was observing a great blue heron when the bittern’s squawking attracted my attention and I saw it land on a dock across the narrow creek from my position.